I disagree that the clean up is detrimental to Wikipedia. I like to browse Wikipedia for new programming languages, and it is very difficult for me to do so when the "good stuff" is buried in WP's lists and categories. More information is not necessarily better :(
Do you assume that everyone uses it for the same purpose?
What makes you think that is a valid reason for "cleaning" up the articles?
In the case of Nemerle, a cursory search of academic and practitioner sites demonstrates it deserves a Wikipedia page. Put it back and go hack on that better wikipedia UI you mentioned.
I remember, before Wikipedia, there was a big debate on the original C2 Wiki about the usefulness of category pages. There is a fairly widespread opinion that categories are a waste of time, because no ontology can usefully classify the body of information that's out there. While it's natural to want to categorize things, people inevitably use very different systems of categorization (as seen by the dozen or so tags that many Wikipedia pages get), and so they'll never be useful to more than a small subset of people. See also Shirky - "Ontology is Overrated":
At the time I left the C2 community, the debate was still raging, but there were still a number of vocal anti-category people. Evidently Wikipedia went the opposite way, but I'd argue that whether it's policy or not, categories are still useless. I always enter Wikipedia via Google; I browse around within it by hyperlinks. The value of Wikipedia is as a store of content, and not as a form of organization.
Category pages are useful as a supplement to good (not-deleted) primary pages.
I usually dislike and cringe at whinging about downvotes, but I think whatever pattern of thought is at work in such a decision is genuinely relevant to the topic at hand.
Category too crowded? Sure let's just delete a few.
May I suggest you just add a new category for "notable programing languages"?